Method of hydrolyzing protein materials



Patented Nov. 23, 1943 m-rrrron or nrnaomrzmo rnornnv marnmans FrederickC. Berswortli, Verona, N. 1., assignor to The Martin Dennis Company,Newark, Neal, a corporation of New Jersey No Drawing. ApplicationOctober 24, 1940,

Serial No. 362,613

4 Claims.

This invention relates to chemistry and more particularly to organicchemistry and has for its object the provision of an improved method ofhydrolyzing organic compounds. Another object is to provide an improvedmethod of hydrolyzing proteins to amino acids. Still another object isto provide means to maintain a substantially constantoxidation-reduction potential during hydrolysis reactions. Other objectsand advantages will be apparent as the invention is more fullyhereinafter disclosed.

In accordance with these objects, I have discovered that in manyhydrolysis reactions the organic material being subjected to hydrolysis,the hydrolyzed product and the intermediate products formed duringhydrolysis are each sensitive to oxidation and reduction, and thatoxidation and reduction reactions on these said products markedlyinterfere with the progress of the hydrolysis reaction and the ultimatekind, quantity and quality of the yield obtained and that,

the oxidation and/or reduction products produced seriously interferewith the purification and isolation of the ultimate hydrolyzed product.

I have found that by conducting or carrying out the hydrolysis reactionat a substantially constant or fixed oxidation-reduction potential thedifficulties heretofore experienced in obtaining satisfactory hydrolysisof organic compounds are substantially eliminated.

As one specific embodiment of the present invention but not as alimitation of the same, the adaptation of the present invention to thehydrolysis of protein to amino acid will be described. Heretofore in theart, it has been proposed to hydrolyze protein into amino acid bydigesting the protein with caustic alkali solution at elevatedtemperature. Under these conditions it iscommonly accepted that water isadded to the linkage of the protein resulting in the formation --COOHand HzN-C- compounds. However, protein is a naturally occurring organiccompound and while recognized generally as being an anhydride of aminoacid it is known to be associated with other organic and inorganiccompounds that interfere with the conversion of the protein byhydrolysis into amino acids and the recovery of the acids from theresultant hydrolyzed mixture. Examples of materials commonly known to beprotein materials are the group of materails identified as soy beanmeal,

Each of these materials when subjected to hydrolysis are converted atleast in part into amino acids. The yield of such acid and the specifickind and qualtiy of acid obtained however varies widely even as betweensuccessive batches of material from the same source hydrolyzedsubstantially identically. By the practice of the present invention,however, substantially reproducible results may be obtained inhydrolyzing successive batches of the same material and the hydrolysisreaction itself becomes adapted to practice on a continuous orsuccessive large scale batch production basis with relatively highpercentage yields of amino acids of consistent composition, therebygreatly simplifying subsequent purification and isolation of the acidsfrom the hydrolysis residues and from each other.

I have found that by introducing readily oxidizable and reduciblematerial in the reaction mixture of protein and caustic alkali asubstantially constant or fixed oxidation-reduction potentialcharacteristic of the oxidizable-reducible mixture may be obtained inthe reacting proteincaustic alkali mixture which potential, per se, mayvary widely without essential departure from the present invention. Ihave found that in the presence of such a substantially constant orfixed oxidation potential the hydrolysis reaction proceeds normally as atime-temperature reaction at a rate which is determined by thetemperatures and pressure and that the yield of amino acid obtained orconversely the losses incident to oxidation and reduction side reactionsis stabilized and is directly effected by the specificoxidation-reduction potential established by the oxidizable-reduciblemixture employed although within fairly wide ranges of potential theamino acid yields are consistently higher than those heretofore obtainedin the absence of such oxidizable-reducible mixture employed in thepractice of the present invention.

In order to maintain a substantially constant or fixed oxidationreduction potential in the hydrolyzing protein-caustic alkali reactionmix ture, means must be provided to absorb or to take up the free and/orionized oxygen and the free and/or ionized hydrogen generated in thereaction mixture. This result may be obtained in a plurality of wayssuch as by the use of a multi-valent inorganic compound, such as forexample the well known multi-valent vanadium and manganese salts, by theuse of an organic compound that is more sensitive to oxidation andreductionthan the protein, amino acid or intersugar beet residues,albumin, casein and the like. u mediate hydrolyzed produc P Such as rexample quinhydrone, or by the use of a mixture of oxidizable metal andhydrogen reducible metal compounds.

The latter way is preferred and as a specific embodiment of the same theadaptation of the present invention to the hydrolysis of protein bycaustic alkali in the-presence of a mixture of metallic lead and leadoxide (or alkali plumbate) will be described.

The usual practice in hydrolyzing protein with caustic alkali atelevated temperatures is to mix the protein with the caustic alkalisolution, using a considerable excess of alkali and heating the same toan elevated temperature within the range Mil-200 C. for a prolonged timeinterval effective to complete the hydrolysis reaction.

I have found that by introducing an oxidationreduction potentialstabilizer material or agent comprised of a mixture of lead and leadoxide into the reaction mixture, the oxidation-reduction potential inthe reaction mixture is stabilized or maintained at a value whichresults in relatively low losses incident to oxidation and/or reductionside-reactions involving the protein, amino acids and intermediatehydrolysis products and that in addition substantially all sulfurcompounds normally contaminating the protein are either eliminated fromthe reacting mixture or are fixed in new organic combinationnon-deleterious to the future use to which the amino acids normally areto be applied. As a further advantage, I have found that contrary toprior art experience the hydrolysis reaction may be carried out underpressure ranging from 100 lbs. per sq. inch up to 400 lbs. per squareinch depending upon the temperature employed or the gaseous intermediateproducts produced and heretofore lost, thereby to increase the yield ofamino acids produced and the consistency of composition of said acidsfrom any given protein material.

The amount of the mixture of lead and lead oxide added to any givenhydrolyzing mixture of protein and caustic alkali may be varied widelywithout essential departure from the present invention. The minimumamount appears to be that amount required to absorb the free or ionizedoxygen and hydrogen with sufficient rapidity to prevent the formation ofdeleterious amounts of side reactions products. This factor obviouslyvaries widely depending upon temperature, pressure, protein and relativequantities. As one example of its use, the following may be given of atypical reaction mixture:

Grams Protein (for example soy bean meal) 100 Caustic alkali solution(50%) 160 A mixture of finely divided lead and lead oxide inapproximately equal proportions 5 to Sufilcient water to make a totalvolume of 1,000 cubic centimeters (one liter) is added before heatingthe same to within the range of temperatures 140-200 C. in an autoclaveor similar container sealed from the atmosphere. 7

In general in such a reaction mixture it will be found that the initialpressure developed on heating will gradually fall as the hydrolysisreaction progresses to a stationary pressure which on cooling toatmospheric temperatures will be a minus pressure of from 10 to 16inches of mercury. In the absence of the lead and lead oxide such aresult is not obtained.

Whereas, in the above specific example, I have disclosed a mixture oflead and lead oxide in approximately equal proportions, it is believedapparent that these proportions may be varied widely without essentialdeparture from the present invention. It appears necessary only toprovide in the reaction mixture a sufficient amount of each constituentto insure the presence of metal and oxide through the entire hydrolyzingreaction.

In place of metallic'lead other readily oxidizable metals may beemployed, such as copper, nickel, selenium, tellurium and molybdenum.The oxidation potential obtained, however, b the use of these metalswill vary somewhat from that of lead leading to variations in the amountof losses. as one skilled in the art will perceive.

In place of lead oxide or alkali plumbate other hydrogen reduciblemetallic oxide and/or alkali soluble and hydrogen reducible compoundsmay be employed, such as copper, vanadium or molybdenum oxide or alkalivanadates and alkali molybdates, with resultant variation in thereduction potential established in the reaction mixture.

With most protein materials hydrolyzed as hereinabove described,however, I have found that the lead-lead oxide mixture results in thelowestlosses incident to oxidation and reduction side reactionsand forthat reason it is preferred as a stabilizer agent in the practice of thepresent invention. Following hydrolysis in accordance with the presentinvention any lead in solution may be precipitated by subjecting theclear alkaline filtrate to treatment with hydrogen at elevatedtemperatures. Following such treatment the amino acids may be recoveredfrom the alkaline filtrate in any convenient manner heretofore known inthe art.

It is believed apparent from the above description and specificembodiment given that the present invention may be widely varied withoutessential departure therefrom and all such modie fications andadaptations thereof are contemplated as may fall within the scope of thefollowing claims.

What I claim is:

1. In the hydrolysis of amino acid anhydrides to amino acids bydigesting the said anhydrides in an aqueous caustic alkali solution, theimprovement which comprises incorporating within the solution a quantityof an oxidation-reduction potential stabilizer agent consisting of amixture of lead and lead oxide. the amount thereof being at leastsufiiclent to maintain a substantially constant low oxidation-reductionpotential in the said solution throughout the progress of the saidhydrolysis reaction.

2. The method of hydrolyzing the amino acid anhydride content ofnaturally occurring organic compounds known as proteins which comprisessuspending the protein in a caustic alkali solution, incorporatingtherein a proportion of an oxidation-reduction stabilizer agentconsisting of a mixture of lead and lead oxide in total amount at leastsufllcient to maintain a substantially constant low oxidation-reductionpotential in the solution during the progress of the hydrolysisreaction, enclosing the suspension from the atmosphere and heating thesaid suspension to a temperature within the range Mil-200 C. for anextended time interval under pressures ranging from 100 to 400 poundsper square inch.

3. The method of converting the amino acid anhydride content ofnaturally occurring procaustic alkali in the presence of anoxidationreduction stabilizer agent consisting of a mixture of lead andlead oxide, the hydrolysis reaction being conducted in a containersealed from the atmosphere at a temperature within the range 140-200 C.and under the steam pressure generated in the container at thetemperature or heating.

4. In the hydrolysis of proteins by the method comprising suspending theprotein in a caustic alkali solution and heating the solution toelevated temperatures, the improvement which comprises enclosing thesuspension from the atmosphere, heating the suspension to a temperaturewithin the range 140 to 200 C. under the steam pressure generated at thetemperature of heating and maintaining during the entire period of saidheating a substantially constant low oxidation-reduction potential insaid solution thereby substantially eliminating losses of the amino acidhydrolysis product as a result 01' the formation of oxidation andreduction side reaction products.

FREDERICK C. BERSWORTH.

